Humidity analyzer



March 15, 194.

J. C. ALBRIGHT HUMIDITY A ALYZER 5 Sheets-Sheet 1 Filed June 20, 1945Jill] I NQ s gag cf sezolz-Cfllbtzgz WW M Mai.

March 15, 1949. J, c, ALBRlGHT 2,464,546

HUMIDITY ANALYZER Filed June 20, 1945 5 Sheets-Sheet 2 March 15, 1949.J. C.ALBR1GHT 2,464,546

HUMIDITY ANALYZER Filed June 20, 1945 5 Sheets-Sheet 3 cfoseplz duh 511ia Mai-.15, 1949 anaemic. Albris'ht. Bala crowd-Pa, assignor toTheDavison Chemical Corporation, Baitimore, Md.

Application Jirhe 20, 1945, Serial No. 800,500

. This invention relates general to the determination ofthe moisturecontent of air and gases and more particularly has reference to a methodand apparatus for measuringthe dew point temperature of a gas.

It is quite often desirable to ascertain the dew point temperature of agas in order that its moisture content-can'be determined. Heretofore dewpoint temperature determinations have been made by chilling a surfaceand exposing it to a .9 cum. (ems-m vapor laden gas. This procedure hasbeen slow and not flexible enough for wide use.

An object of this invention is to provide an apparatus for determiningthe dew point temperature of. a moisture laden'gas.

' Another object of this invention is to provide an apparatus formaintaining a series oLsurface increments at progressively varyingtemperatures. Still another object of this invention isto provide anapparatus for maintaining a series of surface increments atprogressively varying temperatures and for passing a moisture laden gasover said surface increments.

With these and other objects in view, the present invention resides inthe parts and combina- Haiti! and steps and procedures hereinafter-setf9 h.

- In order to facilitate an understanding of the invention, reference ismade to the annexed draw- Figure 3 is a detailed sectional view of theview box taken on line 3-8 of Figure 1 includingthe conduit. for theflow of the moisture laden gas .2 .der these conditions, the moisturewill condense or deposit upon the cooled surface and the temperature atwhich the initial condensation takes 'place i termed the dew pointtemperature."

Once having ascertained the dew point temperature of a given gas sample,it is a simple matter to determine the moisture-content of the gas atany temperature by calculation or from available tables or charta.- 1 1As hereinbefore indicated,"the present invention is directed to anapparatus and procedure for ascertaining the dew point temperature ofamoisture laden gas. In accordance with the present invention, the dewpoint temperature of .a mositure laden gas is'ascertained by passing thegas through a passage having a plurality of surface increments atdiiferent temperatures, the

- temperatures thereof progressively decreasing in the'direction of gasflow, andascertaining the temperature of the warmest surface'incrementupon which moisturecondenses.

An apparatus suitable for carrying out the present invention isillustrated in the accompanying and the cooling Jacket in heat exchangerelation I thereto. s i

Figure 4 is a fragmentary front elevational view of the view box withparts in section".

{Figure 5 is a sectional view of the view box taken on line 5- of Figure3-.

Figure 6 is adiagrammatic or schematic view showing gas and coolingmedium not circuits and the-electrical circuits.

Figure '1 is a fragmentary view similar to Figure.

' 6 illustrating a modified form of the;- invention.

The present invention is based upon the phenomena of the condensationofmoisture from a moisture laden gas upon a surface cooled low enough tocause the gas in contact therewith to assume a temperature at which themoisture condrawings. As shown more particularly in Figures 3 and 6, theapparatus comprises a view box or gas conduit i, one wall I of which isformed of material of high heat conductivity such as metal and at leastthe opposite wall I of which is formed oi a transparent material such asglass or a transparent synthetic resin through'which any con; densationof moistureupon the. surface of the wall 2 may be observed. Otherportions of conduit I may be constructed of transparent, opaque, or anyotherkind of material. The wall 2 of the view box or gas conduit is"divided into a plurality of increments 2a, 2b, etc.,; as illustrated inFigure 3. These increments of the wall 2 are maintained at differenttemperatures which decrease progressively'in the direetionv of'movementof the moisture laden gas through the conduit I. Maintenance of atemperature gradient along the wall 2 will-be described hereinafter. v

A moisture laden gas, the dew point temperature of which is to beascertained. is drawn from any desired source or location anddeliveredinto conduit 4 which communicates with one port of the casingof a three-way valve 5. Communicat ing with another port of thethree-way valve 5 is a conduit 8 which communicates with-the intake portof a pump-1 driven by a suitable source of power such as the electricmotor 8. .The discharge port of the pump 1 communicates through a line 8with one port of a three-way valve i0 tent thereof is sumcient tosaturate the gas. Unwhich has one of its other ports connected by a r a.v conduit II with the intake iitting l2 oi the gas conduit or view boxI.

The third port of the three-way valve 3 is connected by means-of aconduit II with a gas dehumidifying unit it. This is'to enableatmospheric air or some other gas to be drawn through the dehydratingmaterial in the dehydrator It and then forced by the pump 1 through theview.

box or gas conduit i to clear the wall 2 and any other parts of theconduit l of condensed moisture.

The third portof the three-wayvalve n isprovided for discharge of theair or other gas forced from the pump 1 without passing the same throughthe conduit I.

Wall 2 is cooled by means of a cooling medium circulated through acooling jacket I! associated therewith. As illustrated. the coolingjacket comprises top and bottom walls It and I1 respectively, end wallsi8 and i9, and a rear wall 20. The other wall of the cooling jacket is aportion of the wall 2 of the gas conduit i which is formed of materialhaving a high heat conductivity. Cooling Jacket I is provided with aninlet port 2| and a discharge port 22 so arranged that the coolingmedium passed through the jacket flows in a direction generallycounter-currently with respect to the flow of the moisture laden gasthrough the gas conduit I.

A plurality of baflles 23 extend betweenthe top and bottom walls It andi1 and laterally from the wall 2 to a region spaced from the wall 20 ofthe cooling jacket. It will be noted that the bailles 23 aresubstantially perpendicular to the heat conducting wall 2 and divide thespace within the jacket l5 into a plurality of compartments, eachcorresponding to one of the surface increments 20:, etc. Intermediatethe bames 2s a plurality of baflles 24 is provided. Baflles 24 extendfrom the wall 20 to a region spaced from the wall 2 as clearlyillustrated in Figures 3 to 6 of the drawings.

It will be noted that the arrangement or the baffles 23 and 2t providesa tortuous flow path for the cooling medium through the jacket I! fromthe inlet port 2| to the discharge port 22 thereof.

Cooling jacket i5 is adapted to be filled with a cooling medium such asethyl alcohol. Most commercial anti-freeze liquids for use in thecooling systems of internal combustion engines, etc., may be employed.It is preferable to select a liquid for this purpose that is freeflowing at --100'F. when low temperature refrigeration such as atfordedby solid CO2 is employed. However, when refrigeration at temperatures ofabout 32 F. are employed, the cooling system liquid may be one that isfree flowing at temperatures of about 32 F. or lower. The discharge port22 of the jacket l5 has a conduit 25 communicating therewith which isconnected by a T-fltting to'a conduit 26 which leads to a reservoir 21.Reservoir 21 communicates through a cooling coil 23 and a conduit 29,provided with a valve 30, with the intake of a liquid pump 3| driven byan electric motor 32 brother source of power. Liquid discharging fromthepump 3| is introduced into the Jacket i5 by means of a conduit 33communicating with the intake port 2| of the jacket.

Reservoir 21 is provided with a pressure relieving device 34 whichcommunicates with the reservoir through a tube 35. This serves toprevent the generation of any undue pressure on the liquid circulatingthrough the cooling jacket I! and avoids damage to the unit. Any air orgas entrained in the liquid separates in the reservoir and may bedischarged through the gas release 1 circulating system may be eflectedthrough the drain valve 33. I

Reservoir 21 and cooling coil 23 are positionedwithin a tank 40 which isadapted to be filled with a liquid such as ethyl alcohol or one of thecommercial anti-freeze compounds to a level to cover the cooling coil28. Refrigeration of the liquid within the tank 40 may be effected bythe introduction of pieces of solid carbon dioxide therein. Of course,any other means for cooling the liquid within the tank 40 for producinga cooling effect on the circulating liquid passing through the coil 23may be employed. For in stance, a coil in which a refrigerant isevaporated may be disposed within the liquid in the tank 40. Drainageofliquid from the tank 40 may be effected through-a drain valve 4|.

From the foregoing description, it will be appreciated that the presentinvention provides for the circulation of a cooling medium through thetortuous passage provided within the cooling jacket l5. As the coolingliquid flows from the intake port 2| through the several compartments ofthe tortuous passage in the jacket I! to the discharge port 22, itstemperature is gradually and progressively raised.

In accordance with the present invention, it has been found that a moreeffective temperature gradient along the wall 2 may be obtained byproviding means in the several compartments between the baiiles 23 forapplying heat to the cooling medium as it flows through the tortuouspassage in the jacket it. Any suitable means for applying heat to theliquids during its flow through the cooling jacket may be employed. Oneform of such heating means as shown in the drawings embodies electricheating elements. For positioning the electric heating elements in theseveral compartments between the baiiles 23,-

tubes 42 closed at one end and open at the other end extend through thewall 23 with their closed and disposed within the compartments betweenthe bailles 23. It has been found effective to position the tubes 43within the baffles 24 or to form the same integrally with said baiiies24 as illustrated in the several figures of the drawings. With thisconstruction, electric heating elements 43 may be disposed within thetubes 42 so as to be securely sealed from the liquid circulating throughthe jacket IS.

The electrical heating elements 43 are connected as diagrammaticallyillustrated in Figure 6 of the drawings. One terminal of each element isconnected to a common conductor 44 which in turn is connected by thelines 45 and 46 with one pole of a double pole double throw switch 41.One group of said heating elements 43 have their other terminalsconnected to a common conductor 48 which is connected by lines 43 and43' with diagonally disposed poles of the switch 41. The other group ofthe electric heating elements have their other terminals connected to acommon conductor 50 which in turn is connected by a line II to one bladeof the double throw double pole switch and through a control switch I2to a power was.

'5 I line 53. The other'blade of the switchisalso connected through thecontrol switch 82 to the powerline 53. with this connection of theelec-' tric heating elements 48 to the power line 88, all of the heatingelements may be connected in parallel with each other or the heatingelements of each of the two groups may be connected in parallel, withone group connected in series with the other group. Thus,- full linepotential may be applied to each of the heating elements or onehalf offull line potential may be applied to the heating elements. A telltalelamp I4 is connected across the conductors 45 and 48 to indicate whetherthe heating elements are operating on full line potential or one-halffull line potential. 3 The power line 53 is'a branch of a main line I 55controlled by main switch 88 and is equipped with a control switch 51 sopositioned that when said switch 51 is closed, power is supplied fromthe main line 55 to the electric motor 32 and also tothe heatingelements 43. With this arrangement, whenever ,the heating .elements areenergized the motor 32 for circulating the cooling medium will also beenergized to provide for circulation of said medium and thereby avoidoverheating of said elements 43.

v Another branch line 58 equipped with a control switch 59 is providedfor energizing the motor 8 which drives the pump 1. Lamps 60 posi-.tioned to illuminate the view box or gas conduit I are in acircuit 8|controlled by. switch 52 and connected to the power line 53. Anotherlamp 54 is connected in a circuit 65 provided with a control switch 66and connected across the power line '53. The purpose of lamp 84 will bereferred to hereinafter.

, The top wall I6 of the cooling jacket I is provided with a series ofopenings surrounded by upstanding tubes 51 providing access to each ofthe compartments within the cooling jacket I5 between the baffles 23.Extending through each of the tubes 61 is a thermometer 68 or,othertemperature indicating device for indicating the temperature of thecooling medium within the several compartments formed between thebaiiles 23. A sealing device 69 which as shown comprises a short sectionof rubber tubing, provides an effective seal between the upstandingportion of the tube 61 and the thermometer 68.

' To facilitate reading of the temperatures indicated by thethermometers 68, the light bulb 84 is positioned as illustrated inFigures 1 and 2 of the drawing, a suitable reflector or shield beingprovided if desired. It will also be noted that the bulbs 60 forilluminating the view box I are suitably positioned and provided with ashield or reflector.

The entire apparatus including piping and wiring is assembled within acabinet ID as illustrated in Figures 1 and 2 of the drawings. It will benoted that a panel II is provided on which the several switches andvalve operating knobs are mounted.

With the structure herein described, it will be appreciated that inusing the apparatus the surface of the 'wall 2 within the gas conduit Iwill have a deposit of moisture formed thereon. Before reusing theapparatus for determining the dew point temperature of another sample ofgas, the valve 5 is positioned so that the gas drawn into the pump 1will flow through the dehydrator I4. Dehydrated gas is thus forcedthrough the gas conduiti and removes all condensation on the walls ofsaid conduit.

The apparatus is then ready for analysis of a gas conduit I.

new sample of gas which with the valve 8 in the proper position is drawnthrough conduits 4 and 8 into the pump and then passed through the Asthe moisture laden gas, the dew point temperature of which is to beascertained, flows through the conduit I, a deposlt'of moisture willtake place on the inner surface of the wall 2. The temperature of thewarmest portion of the wall 2 on which condensation takes (see Figure'7) in which instance a temperature I responsive element 28a would bepositioned in the line 29 just before the intake to the pump iii toinsure that the temperature of the liquid supplied to the pump would besubstantially constant. It is also within the concept of the presentinvention to replace valve 38 or both valves 30 and 38- withthermostatically controlled valves, the prin-. cipal feature of thevalves being to insure the supply of liquid at a substantially constantselected temperature to the intake port 2I of the cooling jacket I5. Y

To ascertain the dew point temperature of a moisture laden gas inaccordance with the present invention, solid carbon dioxide is added tothe liquid in tank 40 and the pump 3I is placed in operation by closingthe switch5'l. By proper adjustment of the valves 30 and 38, thetemperature of the liquid entering the jacket I5 is brought to thedesired level and then switches 52 and 41 are closed to obtain thedesired heating effect from the heating elements 43. By readjust'ing thevalves 30 and 38 as required, the temperature of the liquid entering thejacket I5 may be adjusted to any desired value between the limits of -60F. and F. Variation of the position of valve 38 will change the gradientof temperature from the inlet 2I to the outlet 22 of the jacket I5. Itis desirable but not necessary to have the heating capacity of all ofthe heating elements 43 uniform which will result in a uniform gradientin temperature throughout the jacket I5.

After the temperatures of the various portionsof the cooling jacket areadjusted to the desired levels, the air pump I is placed in operation byclosing switch 59. With the valves 5 and III in the position shown inFigure 6, a sample of air taken in through the tube 4 will be passedthrough the view slot or conduit I in a direction countercurrently tothe direction of flow of the liquid through the jacket I5. As the airsample passes through the conduit I overthe plate 2, it gradually comesin contact with older and colder portions of said plate until itcontacts a portion which is colder than the dew point of the air. Atthis temperature, the moisture will condense upon this portion of theplate and the colder portions thereof. The dew point temperature is thetemperature shown by the thermometer or temperature indicating devicedirectly behind the warmest portion of the plate 2 upon which themoisture condenses. It has been found that the temperature of the viewplate 2 is for all pracflowing in contact therewith. Since thethermometers 68 indicate the temperature of the liquid surrounding thesame, the reading of the thermometerdirectly behind the warmest portionof the plate 2 upon which moisture condenses will be the dew pointtemperature of the sample of air or other gas passing through theconduit I.

In normal operation of the device shown in the drawings, it is desirableto purge the apparatus for a considerable period of time to bring thehygroscopic moisture load of the apparatus from the point of pick-up ofthe sample to the intake fitting l2 in equilibrium with the gas to beanalyzed passing through the apparatus. For this purpose. the gas usedto purge the system may be discharged to waste directly from the thirdport of the valve I 0. After the purging operation, the sample gas to beanalyzed may then be passed through the conduit 6 over the heat exchangesurface 2'.

After determining the dew point temperature of one gas sample, the valvemay be shifted to pass a dehydrated gas through the view slot or conduitl to remove any condensed moisture from the surfaces thereof, therebyplacing the apparatus in' condition for analysis of the next sample.

The amount of refrigerating efiect introduced through the valve 30 mustexactly balance ther modynamically the accumulating heating effect ofthe electric heating elements is taking into account any heat losses orgains through radiation or conduction to surrounding materials oratmospheres to any portion of the liquid circulating system. Thevariable nature of the heat losses or gains makes it desirable to employthe automatic temperature control of the valves 3d and/or 33 to maintaina proper condition of stability.

While reference has been made to the humid,- ity analysis of air it willbe appreciated that the present invention may be employed forascertaining the dew point of any gas laden with any condensible liquid.

From the foregoing description, it will be appreciated that the presentinvention provides a highly effective apparatus and procedure forascertaining the dew point temperature of a moisture laden gas.

The comparison between the clear and fogged surfaces is very sharp anddistinct which enables the operator to determine with greatest accuracythe dew point temperature.

One valuable feature of the present invention is the holding of adjacentsurfaces of the view plate 2 at difierent temperatures. This greatlyfacilitates the observation by the operator of the foggingof portions ofthe plate since the condensate will form on one portion while anadjacent portion at a slightly higher temperature will be free ofcondensate, affording the observer a clear surface with which he cancompare the fogg'ed surface. The presence of an adjacent clear surfacewill enable the observer to easily detect the slightest fogging of thesurface upon which condensate forms.

I claim:

1. An apparatus for determining the dew point temperature of a moistureladen gas comprising an elongated wall of heat conductive material,means for passing a moisture laden gas along one side of the wall, meansforming a cooling jacket on the other side of said wall, a plurality ofbailles extending from said other side 0! the wall dividing said jacketinto a series of compartments extending longitudinally of the wall,means for passing a cooling medium serially through said compartments ina direction generally countercurrently to said moisture laden gas. meansin each compartment for heating said cooling medium and means fordetermining the temperature of the cooling medium in said compartments.

2. An apparatus for determining the dew point temperature of a moistureladen gas comprising an elongated wall of heat conductive material,means for passing a moisture laden gas ing jacket on the other side ofsaid wall, a plurality of bafiles extending from said other, side of thewall dividing said jacket into a series of compartments extendinglongitudinally of the wall. a plurality of baiiles extending from thenposite wall of said jacket intermediate said iii-st mentioned bafiiescreating a zigzag tortuous passage through said jacket, heating meansdisposed at intervals throughout said tortuous passage, means forpassing a cooling medium through said tortuous passage in a directiongenerally countercurrently to said moisture laden gas and means .fordetermining the temperature of the cooling medium in said compartments.

3. An apparatus for determining the dew point temperature of a moistureladen gas comprising an elongated wall of heat conductive material,means for passing a moisture laden gas along one side of the wall, meansforming a cooling jacket on the other side of said wall, a plurality ofbailles extending from said other side of the wall dividing said jacketinto a series of compartments extending longitudinally of the wall, aplurality of bafies extending from the opposite wall of said jacketintermediate said first mentioned bailles creating a zigzag tortuouspassage through said jacket, heating means mounted in association withsaid second mentioned bafiles, means for passing a cooling mediumthrough said tortuous passage in a direction generally countercurrentlyto said moisture laden gas and means for determining the temperature ofthe cooling medium in said compartments.

e. An apparatus for determining the dew point temperature of a moistureladen gas comprising an elongated wall of heat conductive material,means for passing a moisture laden gas along one side of the wall, meansforming a cooling jacket on the other side of said wall, a plurality ofbattles extending from said other side of the wall dividing said jacketinto a series of compartments extending longitudinally Of the wall, aplurality of baiiies extending from the opposite wall of said jacketintermediate said first mentioned baliies creating a zigzag tortuouspassage through said jacket, tubes extending through said secondmentioned wall of the jacket in association with the second mentionedbaiiles and between adjacent ones of said first mentioned bafiles,heating means within said tubes, means for passinga cooling mediumthrough said tortuous passage in a direction generally countercurrentlyto said moisture laden gas and means for determining the temperature ofthe cooling medium in said compartments.

5. An apparatus for determining the dew point temperature of a moistureladen gas comprising an elongated wall of heat conductive material,means for passing a moisture laden gas along one side of the wall, meansforming a cooling jacket on the other side of said wall, a plurality ofheme:

a cooling medium extending from said other side of the wall dividingsaid jacket into a series of compartments extendin; longitudinallyserially through said compartments in a direction generallycountercurrently to said moisture laden gas, means in each compartmentfor heating said cooling medium, and

means having a temperature sensing device extending into eachcompartment adjacent said elongated wall for indicating the temperatureof the cooling medium.

6. An apparatus for determining the dew point temperature of a moistureladen gas comprising an elongated wall of heat conductive material,means for passing a moisture laden gas along one side of the wall, meansforming a cooling jacket on the other side of said wall. a plurality ofbaiiies extending from said other side of the wall dividing said jacketinto a series of compartments extending longitudinally of the wall,means for passing a cooling medium serially through said compartments ina direction generally countercurrently to said moisture-laden gas, meansin each compartment for heating said cooling medium, said jacket havinga plurality of openings providing access to the compartments adjacentsaid elongated wall, temperature indicating devices extending throughsaid opening, and means for sealing said temperature indicating devicesin said openings. 1

7.- An apparatus for determining the dew point temperature of a moistureladen gas comprising a gas conduit having a heat conducting wall and atransparent wall to provide visibility of the surface of the heatconducting wall within said conduit, a gas pump having an intake and adischarge, a gas dehydrator, a sample tube, means for selectivelyconnecting said pump intake to said dehydrator or sample tube, means forselec-. tively connecting the discharge of the pump to one end of saidgas conduit and to the atmosphere, a cooling jacket including said heatconducting wall as a part thereof, a cooling device, a pump forcirculating a cooling medium through said cooling device and jacket in adirection generally countercurrently to said gas, means in said jacketfor heating said cooling medium during its flow through said jacket, andmeans for determining the temperature of said heat conducting wall alongits length.

8. An apparatus for determining the dew point temperature of a moistureladen gas comprising a gas conduit having a heat conducting wall and ofthe wall, means for passing a transparent wall to provide visibility ofthe surface of the heat conducting wail within said conduit, a gas pumphaving an intake and a dis-. charge, a gas dehydrator, a sample tube,means for selectively connecting said pump intake to said dehydrator orsample tube, means for selectively connecting the discharge of the pumpto one end of said gas conduit and to the atmosphere, a cooling jacketincluding said heat conducting wall as a part thereof, a cooling device,a pump for circulating a cooling medium through said cooling device andjacket in a direction generally countercurrently to said gas, means insaid jacket for heating said cooling medium during its flow through saidjacket, a by-pass about said cooling, device, means for controlling theflow of cooling medium throughsaid cooling device and through saidby-pass, and means for determining the temperature of said heatconducting wall along its length.

9. An apparatus for the determination of the dew point temperature of amoisture laden gas comprising a gas conduit having a heat conductingwall and a transparent wall, a cabinet supporting said conduit forobservation, means for circulating a cooling medium in heat exchangerelation with said heat conducting wall, means for heating said coolingmedium while circulating in heat exchange relation to said heatconducting wall, means for indicating the temperature of said coolingmedium while circulating in heat exchange relation with said heatconducting wall and positioned for observation, means for passing a gasthrough said gas conduit, and means for controlling the temperature ofthe cooling medium and the flow of gas through said conduit, all of saidmeans being mounted in said cabinet.

JOSEPH C. ALBRIGHT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Number Number Date 632,680Germany July 11, 1936 Great Britain Mar. 18, 1943

